This invention relates to an engine control apparatus, and, in particular, to an electronic control device which uses a microprocessor for performing control computations of the amount of fuel to be injected, by effectively using an air intake flow measurement signal.
When an engine is controlled by an electronic control device such as a microprocessor, the operating state of the engine is always monitored, the fuel injection amount in relation to the operating state of the engine is computed, and the amount of fuel is injected.
The monitoring means for controlling the running of the engine in this way, include rotation speed sensors, temperature sensors, and throttle opening sensors, etc. There is also an apparatus for measuring the intake air flow rate for direct computation of the fuel injection quantity. Heat-wire type intake air flow sensors are commonly used for apparatuses having this kind of purpose. These sensors are provided in the intake pipe and comprise a heat sensitive element which is electrically heated. Namely, this heat sensitive element is heated by electricity and cooled by the flow of air in the intake pipe, the thermal variation characteristics of the element corresponding to the intake air flow.
The electronic control unit for the engine typically comprises a microcomputer. In order to compute the fuel injection quantity suitable for the running state of the engine, it is desirable that the detection signals supplied to the control unit be digital. This means that the air flow measurement signal from the air flow measuring device should be digitalized.
In consideration of this, the air flow signal is in pulse form and the measured air flow is expressed as the pulse width of the signal. This kind of measurement signal can be effectively used for computations by the microcomputer by turning the air intake flow into a numerical value by the use of a clock signal to turn the pulse width into a numerical value.